Including 0 in formula (#DIV/0!)

Hi all,

I am trying to create a marksbook that will ignore blank cells and calculate a percentage based on the amount of tasks completed.
So far I have managed to get it all working EXCEPT if I enter 0 as a value.

For example, suppose there are two tasks, both of equal value. If a person was to get 100% for the first task, and 0 for the second task, you would expect the total to be 50%. I cannot get my formula to recognise that a 0 has been entered. Can anyone please help?

(Cells F5:T5 are what the task is out of. Cells F6:T6 is the weighting. I want to be able to enter a 0 in cells F8:T8 to include it in the final percentage.)

CODE:

=IF(AND(ISBLANK(F8),ISBLANK(G8),ISBLANK(H8),ISBLANK(I8),ISBLANK(J8),ISBLANK(K8),ISBLANK(L8),ISBLANK(M8),ISBLANK(N8),ISBLANK(O8),ISBLANK(P8),ISBLANK(Q8),ISBLANK(R8),ISBLANK(S8),ISBLANK(T8)),"",(SUM((IF(LEN(TRIM(F8))=0,,SUM((F8/$F$5)*$F$6/100))+IF(LEN(TRIM(G8))=0,,SUM((G8/$G$5)*$G$6/100))+IF(LEN(TRIM(H8))=0,,SUM((H8/$H$5)*$H$6/100))+IF(LEN(TRIM(I8))=0,,SUM((I8/$I$5)*$I$6/100))+IF(LEN(TRIM(J8))=0,,IFSUM((J8/$J$5)*$J$6/100))+IF(LEN(TRIM(K8))=0,,SUM((K8/$K$5)*$K$6/100))+IF(LEN(TRIM(L8))=0,,SUM((L8/$L$5)*$L$6/100))+IF(LEN(TRIM(M8))=0,,SUM((M8/$M$5)*$M$6/100))+IF(LEN(TRIM(N8))=0,,SUM((N8/$N$5)*$N$6/100))+IF(LEN(TRIM(O8))=0,,SUM((O8/$O$5)*$O$6/100))+IF(LEN(TRIM(P8))=0,,SUM((P8/$P$5)*$P$6/100))+IF(LEN(TRIM(Q8))=0,,SUM((Q8/$Q$5)*$Q$6/100))+IF(LEN(TRIM(R8))=0,,SUM((R8/$R$5)*$R$6/100))+IF(LEN(TRIM(S8))=0,,SUM((S8/$S$5)*$S$6/100))+IF(LEN(TRIM(T8))=0,,SUM((T8/$T$5)*$T$6/100)))*100/(SUMIF(F8:T8,">0",$F$6:$T$6)))))

Link for excel doc --> http://www.4shared.com/file/21197544...ARKSBook1.html